Object detection apparatus

ABSTRACT

A passive ultrasonic vehicle detection apparatus for use with a vehicle such as an automobile, truck, or bus for detecting and indicating the presence of other vehicles in predetermined regions rearward of the subject vehicle, for example, in travel lanes adjacent to the travel lane of the subject vehicle or in so-called &#39;&#39;&#39;&#39;blind&#39;&#39;&#39;&#39; zones of the subject vehicle. When a vehicle is present in one of the adjacent lanes or in a blind zone, signals including ultrasonic signals which are generated inherently by the vehicle, for example, due to a combination of factors such as engine and body vibrations, and engine and tire noises, are received by a frusto-conical signal-receiving horn mounted in a rearward location of the subject vehicle and applied to a piezoelectric crystal transducer. The piezoelectric transducer has a predetermined resonant frequency equal to the frequency of particular ultrasonic signals generated inherently by all existing engine-driven road vehicles. The piezoelectric transducer operates in response to the various signals received from the frusto-conical signal-receiving horn to produce an electrical output voltage which is greatest for ultrasonic signals of the predetermined resonant frequency. The output voltage produced by the piezoelectric transducer is then applied to a resonant circuit tuned to the predetermined resonant frequency to achieve the desired system bandwidth. The output signal produced by the resonant circuit is amplified and applied to an astable multivibrator which operates to produce a train of output pulses for periodically applying the vehicle battery voltage to an integrator circuit. The integrator circuit operates to integrate the voltage pulses received thereby and to operate a driver circuit when a predetermined threshold voltage level is achieved. The driver circuit operates a lamp or other indicator to indicate the presence of the vehicle in the adjacent lane or blind zone.

O Umted States Patent [151 3,681,750 Larka [451 Aug. 1, 1972 [54] OBJECTDETECTION APPARATUS present in one of the adjacent lanes or in a blindzone, 72 I t I t E. L k B signals including ultrasonic signals which areor at mgton Mass generated inherently by the vehicle, for example, dueAsslgneei GTE Laboratofl Incorporated to a combination of factors suchas engine and body [22] Filed: July 2, 1970 vibrations, and engine and tre noises, are received by a frusto-comcal signal-receiving horn mountedIn a PP 51,758 rearward location of the subject vehicle and applied to apiezoelectric crystal transducer. The piezoelectric 52 us. CI. ..340/l611,340/31 R, 340/261 transducer has a I imam i f 51 Int. c1. ..H04b11/00 equal the mummy Pamcula' [58] Field of Search "340 R l T 6 R 16 R,l 5 generated inherently by all existmg engine-driven road 340/34 31 R,258 D 261 vehicles. The piezoelectric transducer operates in response tothe various signals received from the frusto-conical signal-receivinghorn to produce an [56] References Cited electrical output voltage whichis greatest for ul- UNITED STATES PATENTS trasonic signals of thepredetermined resonant frequency. The output voltage produced by the3,159,807 12/1964 Asbury, Sr. ..340/6 piezoelectric transducer is thenapplied to a resonant 3,253,457 5/1966 Pakala et al. ..340/i5 circuittuned to the predetermined resonant frequency 3,268,856 8/1966 Wallen,J1 5 to achieve the desired System bandwidth. 3,l58,835 11/1964 Hipkms..340/34 ABSTRACT A passive ultrasonic vehicle detection apparatus foruse with a vehicle such as an automobile, truck, or bus for detectingand indicating the presence of other vehicles in predetermined regionsrearward of the subject vehicle, for example, in travel lanes adjacentto the travel lane of the subject vehicle or in so-called The outputsignal produced by the resonant circuit is amplified and applied to anastable multivibrator which operates to produce a train of output pulsesfor periodically applying the vehicle battery voltage to an integratorcircuit. The integrator circuit operates to integrate the voltage pulsesreceived thereby and to operate a driver circuit when a predeterminedthreshold voltage level is achieved. The driver circuit operates a lampor other indicator to indicate the presence of the vehicle in theadjacent lane or blind zone.

blind zones of the sub'ect vehicle. When a vehicle is 8 Claims, 3Drawing Fi ures f 5 Hum" fitmsomc slcnu PROCESSING cmcun HORN 15 iunroHULTl-STAGE nssorunr LINEAR ransom i cmcun AMPLIFIER cmcun (40Khz)CIRCUIT I I V I 23 2s 2? 29' s l Muuiiiiiiion swncn mtrcnum nmvrn icmcun cmcun CIRCUIT 000011 I I (I0 Khz) e t I VEHICLE amrmr PATENTEDAUG1 I972 SHEET 1 BF 2 FigA u INVENTOR VINCENT E. LARKA 1 BY fa X hPATENTEUMJB I I972 SHEET 2 [IF 2 Fig 2.

29} e INDICATOR FRUSTUM HORN VEHICLE BATTERY VOLTAGE (e.q.|2V)

Fig. 3.

1 OBJECT DETECTION APPARATUS BACKGROUND OF THE INVENTION other vehiclesin predetermined regions or zones rear- 1 ward of the subject vehicle.

It is often necessary that the operator of a vehicle such as anautomobile, truck, or bus know whether another vehicle is approachingthe subject vehicle from behind in an adjacent lane or is present in ablind" zone before making a lane change or taking other appropriateaction. This type of information is particularly useful to operators ofmany types of trucks and buses where interior rear view mirrors, such ascommonly used in automobiles in conjunction with side rear view mirrorsfor detecting vehicles approaching from the rear, cannot be used due tothe size or construction of the vehicle. In such cases, reliance ispresently placed almost entirely on one or more exterior side rear viewmirrors located on each side of the vehicle.

While side rear view mirrors, whether for automobiles, trucks, or buses,provide a certain amount of useful information to an operator, the sizeand location of such mirrors severely restrict the rear field of view toa very small region. The rear field of view that side rear view mirrorsare capable of providing is even further limited under poor weatherconditions, as in rain, snow, or fog. In addition, side rear viewmirrors require frequent adjustment to be fully effective.

A variety of other object detection arrangements have been proposedheretofore in the prior art for use with a vehicle for detecting andindicating the presence of vehicles approaching the subject vehicle fromthe rear. In one such system which is active in nature, atransmitter-receiver arrangement is carried by a vehicle fortransmitting sonic or ultrasonic time-spaced or continuous-wave signalsin a rearward direction and for receiving and processing the signalsreflected from an object present in the path of the transmitted signal,such as a vehicle, thereby to provide an indication to the operator ofthe presence of the object. A significant disadvantage of such a systemis that it is unable to dis criminate between the particular targetwhich it is desired to detect, that is, an unseen vehicle approachingfrom the rear, and fixed objects such as signs, fences, trees, and thelike. Thus, all objects appear to an operator as targets. While it hasbeen proposed in the prior art to solve the abovementioneddiscrimination problem by means of apparatus such as Doppler-shiftapparatus, such apparatus is complicated and very costly, particularlywhen considered for use in high-volume, mass-produced vehicles, such asautomobiles and trucks, where cost is an important factor. Anotherdisadvantage of active systems of the above type is that they requireboth transmitting and receiving apparatus, thereby adding to systemcosts.

In addition to the abovedescribed active systems, it has been proposedin the prior art, for example, in burglar alarm systems, to detect thepresence of an unauthorized individual in a predetermined area bydetecting a particular frequency or frequencies present in noisesproduced by the individual while in the predetermined area. Asignificant disadvantage of systems of this type, when considered foruse in vehicle-detection applications, is that focusing is limitedinasmuch as sources outside or beyond the particular area of interestmay also cause a system response. In addition, in those systems wherethe time duration or amplitude of the noises to be detected are notsignificant factors to be monitored, improper system operation can occurdue to random or spurious low-level background noises or due to shockstimuli.

BRIEF SUMMARY OF THE INVENTION Briefly, in accordance with the presentinvention, a passive ultrasonic object detection apparatus is providedfor use with a first object for detecting and indicating the presence ofanother object in a predetermined region adjacent to the first objectand which avoids many of the shortcomings and problems associated withprior art object detection apparatus such as described hereinabove. Aswill become readily apparent hereinafter, the primary object and purposeof the present invention is to detect and indicate the presence ofobjects which are inherently capable of generating signals includingultrasonic signals, for example, automotive vehicles. The ultrasonicobject detection apparatus of the present invention is passive in naturein that it does not require an active transmitter, carried either by asubject object or by an object to be detected. Thus, where the objectsof interest are vehicles, many of the object discrimination problemsassociated with prior an active object detection systems 7 are avoided.

The passive ultrasonic object detection apparatus in accordance with thepresent invention includes a signal-receiving means associated with afirst object for receiving the signals inherently generated by anotherobject when the other object is present in a predetermined region ofsurveillance adjacent to the first object. Signals inherently generatedby the other object are received by the signal-receiving means only whenthe other object is present in the predetermined region of surveillance,thereby preventing the occurrence of a response by the apparatus of theinvention due to an object outside or beyond the particular area ofinterest, that is, outside or beyond the predetermined region ofsurveillance. The geometrical configuration of the predetermined regionof surveillance is determined by the signal-receiving means. The varioussignals, including ultrasonic signals, received by the signal-receivingmeans when an object to be detected is present in the predeterminedregion of surveillance adjacent to the first object are applied to aprocessing means coupled to the signal-receiving means. The processingmeans operates to process the ultrasonic signals received from thesignal-receiving means to provide an indication of the presence of theother object in the predetermined region of surveillance.

Since, in accordance with the present invention, ultrasonic signals aredetected and-processed, these ultrasonic signals being produced in thecase of road vehicles regardless of the nature of existingweatherconditions, many of the problems associated with the use of vehicularrear-view mirrors or other prior art visual aids in bad weatherconditions, and blind-spot problems as well, may be effectively avoidedby the present invention. In addition, the passive ultrasonic objectdetection apparatus of the invention may be em ployed effectively byobjects such as trucks and busses regardless of size or nature ofconstruction.

BRIEF DESCRIPTION OF THE DRAWING Additional objects, features, andadvantages of passive ultrasonic object detection apparatus inaccordance with the present invention will be apparent from thefollowing detailed discussion and the accompanying drawing in which:

FIG. 1 illustrates a passive ultrasonic vehicle detection apparatus inaccordance with the present invention as employed with an automobile todetect and indicate the presence of other automobiles in travel lanesadjacent the travel lane of the subject automobile or in blind zones ofthe subject automobile;

FIG. 2 is a top view of the arrangement shown in FIG. 1; and

FIG. 3 is a detailed block diagram of a passive ultrasonic receivingarrangement employed in the passive ultrasonic vehicle detectionapparatus of FIG. I.

GENERAL DESCRIPTION FIGS. 1 and 2 Referring to FIGS. 1 and 2, there isshown a passive ultrasonic vehicle detection apparatus 1 in accordancewith the present invention as employed with an automobile 2. Asindicated in FIGS. 1 and 2, the passive ultrasonic vehicle detectionapparatus 1 comprises a pair of identical passive ultrasonic receivingarrangements la, each comprising, in a series arrangement, asignal-receiving horn member 4, an ultrasonic signal processing circuit5, and an indicator 6. Although the signal-receiving horn members 4 mayassume a variety of possible physical configurations and be physicallymounted at a variety of rearward locations of the automobile 2, it ispreferred that each of the signal-receiving horn members 4 have afrusto-conical (or frustum) configuration, as shown more clearly in FIG.3, and be positioned within a small opening provided in thecorresponding rear tail-light assembly A. Furthermore, to provideoptimum effectiveness, the signalreceiving horn members 4 should cantoutwardly slightly from the travel lane C of the automobile 2 toward theadjacent right and left travel lanes R and L. With the aboveconfiguration and positioning for the signal-receiving horn members 4,corresponding zones or regions of surveillance 8 of essentially the sameconfiguration as the signal-receiving horn members 4 are establishedrearwardly of the automobile 2 and adjacent the right and left lanes Rand L and enveloping any existing rear blind zones of the automobile 2.

As will be described in detail hereinafter, when an approaching vehicleenters one of the regions of surveillance 8, such as an automobile 10 asshown in FIGS. 1 and 2, and only at such time, the correspondingsignal-receiving horn member 4 receives various signals includingultrasonic signals which are generated naturally and inherently by thevehicle. These signals are produced, for example, due to a combinationof factors such as engine and body vibrations, engine, tire, and windnoises and, in general, any other noises associated with the vehicle.Thus, the signal-receiving horn member 4 listens for a vehicle presentin its associated region of surveillance 8. The various signals receivedby the signal-receiving horn member 4 from the vehicle are applied tothe associated ultrasonic signal processing circuit 5, and theultrasonic signals are processed thereby to energize its associatedindicator 6 to indicate to the operator of the automobile 2 the presenceof the vehicle in the associated region of surveillance 8. Theindicators 6 shown in FIGS. 1 and 2 may be placed within the instrumentpanel or on the dashboard of the automobile 2 or in any other suitablelocation. The ultrasonic signal processing circuit 5 employed in each ofthe passive ultrasonic receiving arrangements l a of FIGS. 1 and 2 isshown in greater detail in FIG. 3.

As shown in FIG. 3, the ultrasonic signal processing circuit 5 includesa piezoelectric crystal transducer 15, a tuned resonant circuit 17, amulti-stage linear amplifier circuit 19, a trigger circuit 21, asastable multivibrator circuit 23, a switch circuit 25, an integratorcircuit 27, and a driver circuit 29. The operation of the ultrasonicsignal processing circuit 5 of FIG. 3 is as follows.

When a vehicle such as an automobile enters the region of surveillance 8of the signal-receiving horn member 4, for example, as indicated by theautomobile 10 in FIGS. 1 and 2, the various signals including ultrasonicsignals produced naturally and inherently by the vehicle are received bythe signal-receiving horn member 4. As indicated previously and as shownin FIG. 3, the signal-receiving horn member 4 preferably has afrusto-conical (frustum) configuration. Some typical dimensions for thisparticular configuration are: inside diameter of larger opening,approximately 1.75 inches; inside diameter of smaller opening,approximately 0.75 inch; and length of central longitudinal axis,approximately 3 inches. For these particular dimensions, and referringto FIGS. 1 and 2, a cone shaped region of surveillance is produced whichis approximately 30 feet long (measured along the central longitudinalaxis) and which has a diameter at the larger (base) end of approximately15 feet. The various signals received by the signal-receiving hornmember 4 are applied to the piezoelectric crystal transducer 15. Toinsure that the piezoelectric crystal transducer 15 receives all of thesignals collected by the signal-receiving horn member 4, it isphysically positioned adjacent the smaller of the two openings of thesignal-receiving horn member 4.

The piezoelectric crystal transducer 15 preferably has a fundamentalexcitation or resonant frequency of 40 kilohertz. This particular valueof excitation frequency is preferred inasmuch as all existingenginedriven road vehicles, including automobiles, trucks, buses,motorcycles, and motorbikes, naturally generate ultrasonic signals(among other signals, both ultrasonic and non-ultrasonic) having afrequency of 40 kilohertz. In addition, a 40 kilohertz resonantfrequency is sufficiently removed from the audio frequency range so asto preclude undesirable operation of the ultrasonic signal processingcircuit 5 by spurious signals in the audio range. However, sinceultrasonic signals of other frequencies are also generated naturally byexisting engine-driven road vehicles, for example, 50-60 kilohertz, itis contemplated that the piezoelectric crystal transducer 15 have afundamental excitation frequency other than 40 kilohertz. A particularlysuitable 40 kilohertz piezoelectric crystal transducer and mountingstructure therefor which may be employed in the present invention issold by Massa, lnc., Hingham, Massachusetts, under the designation MK109.

The 40 kilohertz piezoelectric crystal transducer 15 operates inresponse to the signals received via the signal-receiving horn member 4to produce an output voltage which is greatest for ultrasonic signals ofan excitation frequency of 40 kilohertz. Natural harmonics of theultrasonic signals of the fundamental 40 kilohertz excitation frequencyalso cause an output response but to a lesser degree than the ultrasonicsignals of the 40 kilohertz frequency; non-harmonic signals also producean output response but to a lesser degree than the 40 kilohertzultrasonic signals or harmonics thereof. Since the response-frequencybandwidth of the piezoelectric transducer 15 is difficult to control orpredict, and may vary from transducer to transducer due to physicaldimensioning problems associated with the manufacture of piezoelectriccrystal transducers, the output voltage produced by the 40 kilohertzpiezoelectric crystal transducer 15 is applied to the tuned resonantcircuit 17, having a tuned resonant frequency of 40 kilohertz, whichprovides an electrical output signal of the desired system bandwidth. Byway of example, the tuned circuit 17 may include a 40 millihenry coilhaving one end connected in series with the piezoelectric transducer 15and an 82 kilohm resistor connected between the other end of the 40millihenry coil and ground potential, this arrangement providing a 6kilohertz, 6 db bandwidth centered at 40 kilohertz. The output signalfrom the tuned circuit 17 is then applied to the multi-stage linearamplifier circuit 19 and amplified thereby to a level suitable forfurther processing. The multistage linear amplifier circuit 19 maytypically comprise three conventional transistor class A amplifierstages and a conventional transistor class C amplifier stage arranged incascade, with the components of the various amplifier stages beingselected to provide a 100 db( voltage gain.

The amplified output signal produced by the multistage linear amplifiercircuit 19 is applied to the trigger circuit 21 to produce a triggersignal for triggering the astable multivibrator circuit 23 to itspulse-producing state. For most effective operation, the trigger circuit21, which may be implemented by a variety of circuits well known tothose skilled in the art, has an input threshold voltage levelassociated therewith which must be exceeded before producing a triggersignal. In this fashion, lowlevel background noises are prevented fromcausing a system output response. The astable multivibrator circuit 23may be of a conventional transistor design including a pair oftransistors and operable to produce a train of square-wave output pulsesin response to a trigger signal. A particularly suitable and convenientfrequency for the train of output pulses produced by the astablemultivibrator circuit 23 is 10 kilohertz, although suitable operationcan also be achieved with slight modification of the subsequentcircuitry for other frequencies between 1 kilohertz and l megahertz.

The 10 kilohertz output pulse train produced by the astablemultivibrator circuit 23 is then applied to the switch circuit 25, of aconventional design, to switch the vehicle battery voltage, typically 12volts DC, on and ofi at a 10 kilohertz rate and to apply the l2-voltpulses so produced to the integrator circuit 27. The integrator circuit27, which typically includes a conventional parallel-RC circuit, forexample, a 4.7 kilohm resistor in parallel with 35 microfarad capacitor,is arranged to integrate the 10 kilohertz l2-volt pulses produced by theswitch circuit 25 over a period of time equal to the time that a vehicleis in the region of surveillance established by the signal-receivinghorn member 4 and presenting ultrasonic signals to the signal-receivinghorn member 4, and to produce an output signal for energizing the drivercircuit 29 when the voltage developed across the capacitor reaches apredetermined threshold voltage which is indicative of the presence of avehicle in the surveillance region. The threshold voltage is establishedat a value, for example, 4-5 volts, which is above that which would beproduced by the integrator circuit 27 as a result of integrating pulsesinitiated by spurious, random, or background noises received by thesignal-receiving horn member 4 or by shock acoustical stimuli receivedby the signal-receiving horn member 4 and of sufficient amplitude tocause operation of the trigger circuit 21. Thus, the driver circuit 29,which may be a conventional transistorized driver circuit of well-knowndesign, is energized only when a vehicle is present in the region ofsurveillance 8 associated with the signalreceiving horn member 4. Whenthe driver circuit 29 is energized by the integrator circuit 27, theindicator 6 is operated to indicate to the operator that a vehicle ispresent in the associated region of surveillance 8. The indicator 6 maybe a warning light, audible buzzer, or any other suitable indicatingdevice.

MODIFICATIONS Although a vehicle detection apparatus 1 including twopassive ultrasonic receiving arrangements la has been describedhereinabove, it is apparent that fewer or more than two passiveultrasonic arrangements may be used in certain applications. Forexample, it may be desired in certain applications to employ only onepassive ultrasonic receiving arrangement, for example, for detecting andindicating to the operator of a vehicle the presence of rearwardapproaching vehicles in the same lane as the subject vehicle. In otherapplications, it may be desired to add a center-lane passive ultrasonicreceiving arrangement to the right an left lane passive ultrasonicreceiving arrangements described hereinbefore. Other modifications andchanges will be obvious to those skilled in the art without departingfrom the invention as defined by the appended claims.

What is claimed is:

1. A passive ultrasonic object detection apparatus associated with afirst object for detecting and indicating the presence of another objectin a region of surveillance adjacent to the first object, said anotherobject inherently generating signals including ultrasonic signals, saidapparatus comprising signal-receiving means for receiving the signalsinherently generated by said another object when said another object ispresent in the predetermined region of surveillance adjacent to saidfirst object, said signal-receiving means receiving said signals onlywhen said another object is present in said predetermined region ofsurveillance, said predetermined region of surveillance having ageometrical configuration determined by said signal-receiving means; andprocessing means coupled to the signalreceiving means for processing theultrasonic signals received by the signal-receiving means to provide anindication of the presence of said another object in the predeterminedregion of surveillance, said processing means comprising an ultrasonictransducer having a predetermined resonant frequency and arranged toreceive the signals received by the signal-receiving means, saidultrasonic transducer being operable in response to the ultrasonicsignals received from the signal-receiving means to produce an outputvoltage which is greatest for ultrasonic signals of the predeterminedresonant frequency; and circuit means connected to the ultrasonictransducer and operable in response to the output voltage produced bythe ultrasonic transducer to produce an output signal having apredetermined amplitude and duration indicative of the presence of saidanother object in the predetermined region of surveillance, said circuitmeans comprising tuned resonant circuit means connected to theultrasonic transducer and having a tuned resonant frequency equal to theresonant frequency of the ultrasonic transducer, said tuned resonantcircuit means being operable in response to the output voltage producedby the ultrasonic transducer to produce an output signal of apredetermined bandwidth; amplifier means connected to the tuned resonantcircuit means and operable to amplify the output signal produced by thetuned resonant circuit means to produce an amplified output signalhaving a predetermined voltage gain; pulse circuit means connected tothe amplifier means and operative in response to the amplified outputsignal produced by the amplifier means to produce a series of outputpulses of a predetermined frequency; dc voltage supply means adapted toproduce a dc voltage of a predetermined amplitude; switching circuitmeans connected to the pulse circuit means and to the dc voltage supplymeans and operative in response to the series of output pulses producedby the pulse circuit means to switch the dc voltage produced by the dcvoltage circuit means on and off at the predetermined frequency of theseries of output pulses produced by the pulse circuit means thereby toproduce a series of output pulses of the same frequency as the series ofoutput pulses produced by the pulse circuit means and having anamplitude equal to the amplitude of the dc voltage produced by the dcvoltage supply means; and integrator circuit means connected to theswitching circuit means and operable in response to the series of outputpulses produced by the switching circuit means to integrate said pulsesand to produce an output signal having a predetermined amplitude andduration indicative of the presence of said another object in thepredetermined region of surveillance.

2. A passive ultrasonic object detection apparatus in accordance withclaim 1, further comprising:

output means connected to the integrator circuit means and operable inresponse to the output signal produced by the integrator circuit meansto provide a sensible indication of the presence of said another objectin the predetermined region of surveillance. 3. A passive ultrasonic obect detection apparatus in accordance with claim 1 wherein saidultrasonic transducer is a piezoelectric crystal transducer.

4. A passive ultrasonic object detection apparatus in accordance withclaim 3 wherein said pulse circuit includes an astable multivibratorcircuit.

5. A passive ultrasonic object detection apparatus in accordance withclaim 4 wherein:

said signal-receiving means includes a horn member having a frustumconfiguration; and

said predetermined region of surveillance has essentially a frustumconfiguration.

6. A passive ultrasonic object detection apparatus in accordance withclaim 5, further comprising:

output means connected to the integrator circuit means and operable inresponse to the output signal produced by the integrator circuit meansto provide a sensible indication of the presence of said another objectin the predetermined region of surveillance.

7. A passive ultrasonic object detection apparatus in accordance withclaim 6 wherein said another object is an engine-driven vehicle.

8. A passive ultrasonic object detection apparatus in accordance withclaim 6 wherein said first object and said another object are bothengine-driven vehicles and wherein said dc voltage supply means includesa storage battery carried by said first engine-driven vehicle.

1. A passive ultrasonic object detection apparatus associated with afirst object for detecting and indicating the presence of another objectin a region of surveillance adjacent to the first object, said anotherobject inherently generating signals including ultrasonic signals, saidapparatus comprising signalreceiving means for receiving the signalsinherently generated by said another object when said another object ispresent in the predetermined region of surveillance adjacent to saidfirst object, said signal-receiving means receiving said signals onlywhen said another object is present in said predetermined region ofsurveillance, said predetermined region of surveillance having ageometrical configuration determined by said signal-receiving means; andprocessing means coupled to the signal-receiving means for processingthe ultrasonic signals received by the signalreceiving means to providean indication of the presence of said another object in thepredetermined region of surveillance, said processing means comprisingan ultrasonic transducer having a predetermined resonant frequency andarranged to receive the signals received by the signal-receiving means,said ultrasonic transducer being operable in response to the ultrasonicsignals received from the signal-receiving means to produce an outputvoltage which is greatest for ultrasonic signals of the predeterminedresonant frequency; and circuit means connected to the ultrasonictransducer and operable in response to the output voltage produced bythe ultrasonic transducer to produce an output signal having apredetermined amplitude and duration indicative of the presence of saidanother object in the predetermined region of surveillance, said circuitmeans comprising tuned resonant circuit means connecTed to theultrasonic transducer and having a tuned resonant frequency equal to theresonant frequency of the ultrasonic transducer, said tuned resonantcircuit means being operable in response to the output voltage producedby the ultrasonic transducer to produce an output signal of apredetermined bandwidth; amplifier means connected to the tuned resonantcircuit means and operable to amplify the output signal produced by thetuned resonant circuit means to produce an amplified output signalhaving a predetermined voltage gain; pulse circuit means connected tothe amplifier means and operative in response to the amplified outputsignal produced by the amplifier means to produce a series of outputpulses of a predetermined frequency; dc voltage supply means adapted toproduce a dc voltage of a predetermined amplitude; switching circuitmeans connected to the pulse circuit means and to the dc voltage supplymeans and operative in response to the series of output pulses producedby the pulse circuit means to switch the dc voltage produced by the dcvoltage circuit means on and off at the predetermined frequency of theseries of output pulses produced by the pulse circuit means thereby toproduce a series of output pulses of the same frequency as the series ofoutput pulses produced by the pulse circuit means and having anamplitude equal to the amplitude of the dc voltage produced by the dcvoltage supply means; and integrator circuit means connected to theswitching circuit means and operable in response to the series of outputpulses produced by the switching circuit means to integrate said pulsesand to produce an output signal having a predetermined amplitude andduration indicative of the presence of said another object in thepredetermined region of surveillance.
 2. A passive ultrasonic objectdetection apparatus in accordance with claim 1, further comprising:output means connected to the integrator circuit means and operable inresponse to the output signal produced by the integrator circuit meansto provide a sensible indication of the presence of said another objectin the predetermined region of surveillance.
 3. A passive ultrasonicobject detection apparatus in accordance with claim 1 wherein saidultrasonic transducer is a piezoelectric crystal transducer.
 4. Apassive ultrasonic object detection apparatus in accordance with claim 3wherein said pulse circuit includes an astable multivibrator circuit. 5.A passive ultrasonic object detection apparatus in accordance with claim4 wherein: said signal-receiving means includes a horn member having afrustum configuration; and said predetermined region of surveillance hasessentially a frustum configuration.
 6. A passive ultrasonic objectdetection apparatus in accordance with claim 5, further comprising:output means connected to the integrator circuit means and operable inresponse to the output signal produced by the integrator circuit meansto provide a sensible indication of the presence of said another objectin the predetermined region of surveillance.
 7. A passive ultrasonicobject detection apparatus in accordance with claim 6 wherein saidanother object is an engine-driven vehicle.
 8. A passive ultrasonicobject detection apparatus in accordance with claim 6 wherein said firstobject and said another object are both engine-driven vehicles andwherein said dc voltage supply means includes a storage battery carriedby said first engine-driven vehicle.